Salinity, pH, Temperature, Desiccation And Hypoxia Tolerance In The Invasive Freshwater Apple Snail Pomacea insularum
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Pomacea insularum is a tropical and subtropical, ampullariid, freshwater prosobranch snail that is native to slow-flowing rivers and canals in South America. It is a member of the genus, Pomacea, and, like other species in this genus, can be a severe agricultural pest in wetland rice and taro agriculture systems. It has been introduced to the United States, establishing populations in the rice belt region of southeastern Texas. The resistance adaptations of P. insularum were investigated with respect to important physico-chemical parameters including temperature, salinity, pH, emersion, desiccation and progressive hypoxia in order to predict its potential distribution in North America, evaluate its threat to U.S. rice and taro crops and to develop environmentally acceptable non-chemical control and management strategies to prevent its further dispersal in North America. The research results indicated that the main factor likely to limit the macrogeographic distribution of P. insularum in North America was temperature based on its incipient tolerated temperature range of 15.2°-36.6°C. Its 15°C lower lethal limit will restrict its distribution to southern and western coastal regions and Florida in the United States. The tolerances of P. insularum to salinity, pH, emersion, desiccation and hypoxia elucidated in this study can be utilized to develop a risk assessment for this species' microgeographic distribution. Its tolerated salinity range was 0-6.8 which should prevent it from deeply invading estuarine habitats. Its tolerated pH range is 4.0-10.5, which spans that of most freshwater invertebrate and fish species. Its incipient emersion tolerance ranged from 70 days at 30°C and >95% relative humidity (RH) to >308 days at 20°-25°C and 75%->95% RH. Its maximum desiccation tolerance was loss of 58% of total corporal plus extracorporal water. It was a moderate regulator of oxygen consumption when subjected to progressive hypoxia, maintaining a normal oxygen uptake rate down to a critical Po2 of 80-120 Torr depending on temperature. These results indicated that, within its tolerated temperature range, P. insularum, will be most successful in oxygenated, flowing-water habitats and could be controlled by periodic dewatering of natural or wetland aquatic habitats.